1. Field of the Invention
The present invention relates to a brake unit for a bicycle pivotably attached to brake brackets each having a support shaft projecting sideways and a radial seat surface formed in a proximal region of the support shaft. This brake unit comprises:
brake calipers each including:
a boss having a boss bore for receiving the support shaft; PA1 a first end surface extending radially; and PA1 a second end surface disposed axially opposite from the first end surface;
holding means for holding each brake caliper on the support shaft, the holding means having a contact surface extending radially; and
a bush mounted between an inner peripheral surface of the boss bore and an outer peripheral surface of the support shaft;
2. Description of the Related Art
A conventional brake unit is disclosed in Japanese Utility Model Publication Kokai No. 1975-67558, for example. This brake unit includes brake calipers each defining a boss having a bush fitted therein, which bush is longer than the boss. The bush is inserted into a support shaft extending sideways from a brake bracket fixed to a bicycle frame. An end of the bush projecting from the boss is placed in contact with a seat surface extending radially of the brake bracket, and the bush is clamped with a stud bolt at the other end, whereby the brake caliper is pivotably attached to the support shaft. The brake caliper has a brake shoe mounted thereon. When a brake cable is pulled to swing the calipers toward a wheel, the brake shoes contact a wheel rim to apply a braking force to the bicycle.
In such a braking operation, the contact between the brake shoes and the rotating rim generates a force to move each brake caliper along the support shaft of the brake bracket. In order to prevent such displacement of the brake caliper, it is necessary for the conventional brake unit noted above to have the bush securely held between the stud bolt and the radially extending seat surface of the brake bracket. Further, the bush must be pressed hard into a bore of the bush of the brake caliper so that the bush is not slidable along the boss bore. However, the bush could be deformed when pressed hard into the boss bore, thereby impairing circularity of its inner peripheral wall. In this case, the bush press fit in the boss may be reamed though it tends to involve an additional cost. This eliminates the distortion of the inner periphery of the bush resulting from the press fitting into the boss, allows the brake caliper to be assembled to the brake bracket with ease, and realizes a smooth relative rotation between the brake caliper and support shaft.
The above inconvenience can occur not only with the brake unit disclosed in the prior publication cited hereinbefore, but with similar brake units disclosed in U.S. Pat. Nos. 4,754,853 and 5,058,450 and European Laying-Open Patent Publications Nos. 0432268A1 and 0554909.